Shred the papaya in a food processor.
Put the green beans in a large bowl and bruise them lightly with a wooden spoon. Add the tomatoes, scallions, chile pepper and the papaya.
Stir the fish sauce, brown sugar, lime juice and a pinch of salt together in a small bowl, then add it to the papaya mixture and toss to coat. Toss in the cilantro. Let stand 15 minutes. Toss in the peanuts, if using, right before serving.
Recipe courtesy of Rev Run's Sunday Suppers